This disclosure relates to improving the quality of well log data by removing coherent noise.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions.
When a well is drilled into a geological formation, logging tools are used to determine a variety of characteristics of the well. Some logging tools may determine characteristics of the surrounding rock formation and some logging tools may determine when cement has been properly installed in the well to achieve zonal isolation. In the example of cement evaluation, a wellbore may be targeted to produce oil and/or gas from certain zones of the geological formation. To prevent zones from interacting with one another via the wellbore and to prevent fluids from undesired zones entering the wellbore, the wellbore may be completed by placing a cylindrical casing into the wellbore and cementing the annulus between the casing and the wall of the wellbore. During cementing, cement may be injected into the annulus formed between the cylindrical casing and the geological formation. When the cement properly sets, fluids from one zone of the geological formation may not be able to pass through the wellbore to interact with one another. This desirable condition is referred to as “zonal isolation.” Yet well completions may not go as planned. For example, the cement may not set as planned and/or the quality of the cement may be less than expected. In other cases, the cement may unexpectedly fail to set above a certain depth due to natural fissures in the formation.
A variety of acoustic tools may be used to verify that the cement is properly installed. These acoustic tools may use pulse acoustic waves as they are moved through the wellbore to obtain acoustic cement evaluation data at various depths and azimuths in the wellbore. The acoustic cement evaluation data may include not just the signal relating to the quality of the cement, however, but also noise caused by the electronic circuitry of the tool and other sources. Recent developments in well drilling and completion may reduce the strength of the detected signal and/or may benefit from higher precision. Wells are increasingly drilled using heavier drilling fluids and thicker casings, for example, which may attenuate acoustic signals more than lighter drilling fluids and thinner casings. In addition, well casings are increasingly being installed using lighter cements that have acoustic properties more similar to fluids than heavier cements. These lighter cements may be difficult to detect without finer precision. Accordingly, improving the signal-to-noise ratio (SNR) of acoustic downhole tools may enable more accurate and/or precise determinations of cement installation quality.